Caption: Martian atmospheric loss. Animation showing the planet Mars losing its atmosphere by a sputtering process. Atoms are knocked away from the atmosphere due to impacts with energetic particles. This may have helped to drive the Martian atmosphere into space over billions of years. Currently, Mars is a rocky desert world with no surface water. The atmosphere is mostly carbon dioxide and Martian surface temperatures are well below freezing. Most of the water and atmosphere were lost to space, or locked up underground in deposits of ice. NASA's MAVEN (Mars Atmosphere and Volatile Evolution Mission) spacecraft will allow scientists to study how and why Mars lost its atmosphere (and thus its water). It is thought that several processes have had an impact on the process. See clips K004/1390 to K004/1392 for animations of these processes.